This invention relates generally to tools used for removing and replacing valves attached to a wellhead under pressure without shutting in the well; and, more particularly, to improvements in a plug mechanism for use with the tool which may be releasably locked within and sealed with respect to a bore of the wellhead.
The improved plug mechanism of this invention is designed for use on wellhead assemblies to remove and replace wing valves from the side of the casing bowl or spool assemblies. Several devices are known in the art for removing such valves and the like from a wellhead assembly; one such device is shown in U.S. Pat. No. 4,019,541 issued Apr. 26, 1977 to L. Koppl. This patent discloses a wellhead tool capable of placing a plug in a bore of a specially designed T-fitting upstream of the valve to be removed. The use of this tool and plug apparatus is obviously limited to use on new equipment in a system utilizing the same manufacturer's T-fitting, however, it is desirable to have a plug mechanism that can be used in existing and new equipment utilizing universal T-fitting and wellhead designs.
Another such device is shown in U.S. Pat. No. 4,184,504 issued Jan. 22, 1980 to Carmichael et al, and assigned to the same assignee as the present invention, which shows a similar tool and plug arrangement as the present invention. This device utilizes a plug mechanism which is placed in a smooth bore T-fitting upstream of the valve to be removed. The plug mechanism is secured within the bore by use of a plurality of radially movable and pivotally mounted latch members which lock onto the sides of the transverse intersecting bore of the wellhead. However, due to the small diameter bore sizes typically used on side outlets of well-heads (e.g. 3 inches), the diameter of the plug mechanism must be small enough to fit therein and the pivotally mounted latch members can not be economically constructed of material strong enough to withstand the high pressures (up to 30,000 pounds per square inch) and high temperatures (up to 1,500 degrees F.) which are encountered in a wellhead assembly.
It is therefore a primary object of this invention to provide an improved plug mechanism for use with a wellhead for removing and replacing valves on an operating wellhead which overcomes the aforementioned disadvantages of the prior art devices.
It is a further object of the invention to provide an improved plug mechanism having a positive acting latch means to securely lock the plug mechanism within the bore of the T-fitting upstream of the valve to be removed and which can withstand the extremely high wellhead pressures existing therein without deformation of the mechanical parts of the plug mechanism.
It is a further object of the invention to provide a tool and plug mechanism that are usable in smooth bore T-fittings presently used in oil field type and geothermal type wellhead assemblies.
Still, a further object of the invention is to provide a tool for removing and replacing valves on a wellhead assembly wherein the tool has a powerable piston and cylinder arrangement on an operating mechanism that inserts and actuates a plug mechanism having a packing and latching assembly for sealing the bore and fluid flow to the valve to be removed.
Various other objects, advantages and features of the invention will become apparent to those skilled in the art upon examination of the following description of a preferred embodiment of the invention and the accompanying drawings.